The present invention relates to an electrical connector. More specifically, the present invention relates to high input/output density connectors, such as surface mount connectors using ball grid array (BGA) technology.
The recent drive for smaller, more functional electronic equipment, particularly personal portable devices, has created an ongoing need for miniaturization of all components, especially electrical connectors. Efforts to miniaturize connectors have included reducing the pitch between terminals in single or double row linear connectors. This permits a relatively larger number of connections in the ever decreasing space allotted for connectors on circuit substrates. The drive for smaller electronic equipment has also been accompanied by a recent preference for surface mount techniques (SMT) for mounting components on circuit boards. However, because reducing the pitch between terminals increases the risk of bridging adjacent solder pads during the reflow of solder paste, SMT has been pushed to its limits for high volume, low cost operations.
To satisfy the need for increased terminal density in SMT, array connectors have been proposed. In particular, as described in PCT Application No. PCT/US97/18066, filed Oct. 7, 1997, entitled High Density Connector and Method of Manufacture, incorporated herein by reference, ball grid array (BGA) connectors have become a reliable and efficient technique for mounting high density electrical connectors on substrates using SMT. BGA connectors have an insulative connector housing. One side of the connector housing has a matrix of spherical solder balls, positioned to engage the conductive paths of a circuit substrate. The opposite side of the connector housing has a corresponding matrix of contact terminals, which extend through the connector housing and connect electrically to the solder balls. These contact terminals are designed to engage another BGA connector, similarly connected to another substrate, thus permitting board-to-board interconnection. BGA connectors may be used to interconnect a number of various types of circuit substrates, including flexible circuits.
A flexible circuit is a pliable electrical conductor device in which conductive tracings are photolithographed on a base sheet of polyimide or polyester film, such as manufactured and sold by E. I. du Pont de Nemours and Co. under the trademarks xe2x80x9cKaptonxe2x80x9d (U.S. Pat. No. 3,781,596) or xe2x80x9cMylar.xe2x80x9d Because of their light weight and ability to bend and adapt to confined locations, flexible circuits are used in a variety of applications, including portable computers and portable communication devices. In addition, because of their ability to flex resiliently, flexible circuits are used on moving devices, like hard disk drives and compact disk pick-ups. Flexible circuits may be interconnected either to conventional circuit board substrates or to other flexible circuit substrates. There are a number of conventional approaches to accomplish interconnections involving flexible circuits. One conventional approach is to simply solder the flexible circuit to the substrate. This approach, however, makes assembly and disassembly impractical. A second conventional approach is to solder a connector to the flexible circuit for connection with another connector soldered onto the substrate. Presently, however, this approach limits terminal density and requires a stiffener device to be attached to the flexible circuit to withstand the mechanical forces imposed on the connector.
The recent advent of the BGA connector has overcome the problem associated with low terminal density. As a result, the BGA connector has been used in flexible circuit applications. However, because of the dynamic environment of a flexible circuit, the BGA connector was also used in conjunction with a stiffener to be able to withstand the significant mechanical forces between it and the flexible substrate. Notably, these mechanical forces may be of concern when using BGA connectors to interconnect non-flexible circuit substrates as well.
Therefore, a need exists for providing mechanical strain relief to a BGA connector system, without requiring an additional stiffener device.
The disadvantages of prior connector systems are overcome and significant advantages achieved in an electrical connector having a plurality of contacts that are adapted to be electrically connected to a substrate. A first body of reflowable, electrically conductive material is placed on a contact, in order to provide an electrical path between the connector and the substrate. In addition, a second body of reflowable, electrically conductive material is placed on another contact. This second body provides mechanical strain relief between the connector and the substrate. In an alternative embodiment, the contacts of the electrical connector may be arranged in a matrix array. In this alternative embodiment, the second body may be disposed on adjacent contacts forming one or more rows or columns in the array. In addition, the second body may be disposed on adjacent contacts located in one or more corners of the array. A method for providing mechanical strain relief to a connector system is achieved by providing an electrical connector such as described above, and mounting the electrical connector to a substrate.